1. Field of the Invention
The present invention relates to a sheet through type image reading device and a copier having the sheet through type image reading device.
2. Discussion of the Background Art
An image reading device capable of sub scanning an image on an original document by conveying the original document through a fixed reading position is well known. A platen glass is arranged at the reading position to allow a light emitted from a light source arranged inside the image reading position to pass toward the original document located outside thereof and a light reflected from the original document toward the inside thereof. Since the original document passes there through contacting the platen glass in this type of the image reading device during reading the image of the original document, dust sticking to the image surface on the original document unavoidably attracts to the platen glass, and thereby an image signal read therefrom is influenced and an image is deteriorated as a result. This also deteriorates quality of an image formed by another type of an image reading device than the sheet through type. When the original document is fixed and the image reading section is moved in a sub scanning direction to read an image thereof, the dust only causes a spot on the image. Whereas when the sheet through type image reading device is employed, a line is drawn in the direction by the dust.
It is described in the Japanese Patent Registration No. 3573884 and the Japanese Patent Application Laid Open No. 2007-159033 that an original document is conveyed through a reading position keeping a prescribed gap from a platen glass and is read by the image reading device. In such a configuration, the original document can be conveyed avoiding sliding contact with the platen glass. As a result, dust or the like can be prevented from dropping from the image surface side of the original document and attracting to the platen glass at the reading position. Accordingly, the line hardly appears on the image while maintaining the quality thereof.
However, in the above-mentioned several prior arts, the dust or the like dropped therefrom during its conveyance sometimes attracts to the reading position on the platen glass and draws the line on the image.